CHAPTER IV

CONDENSING THE STRAINED OR CRUSHED TOMATOES

Vacuum Pan

Practically all of the tomato products made in this country are cooked in an open kettle under atmospheric pressure—either a copper-jacketed kettle, or a tank with a closed coil. The vacuum pan is used, however, in several plants, and makes a very high grade product—a better product as a rule than can be made by condensing under atmospheric pressure. When tomato juice is condensed in vacuum it boils at anywhere from 54 degrees F. to 175 degrees F., depending upon the degree of vacuum obtained. At sea level, under atmospheric pressure, it boils at 212 degrees F. By employing a low temperature, and condensing rapidly, which can be done in the vacuum pan, the natural bright red color of the tomatoes is affected very little by the cooking. High temperatures and continued boiling are the agents which destroy tomato color as well as flavor. The vacuum pan produces a pulp of not only fine color, but of very fine flavor. The reason the vacuum method is not used more frequently than it is is undoubtedly due to the difficulty in getting the vacuum equipment, and also to the expense of the equipment when it can be obtained.

Types of Open Kettles

The open kettle method produces a very satisfactory product when the proper precautions are taken, and if the cooking and subsequent processes are carried out intelligently, the finished product compares very favorably with that which is condensed in vacuum. The types of kettles in most common use are the copper jacketed kettle, the glass-lined tank with closed copper coil, and the cypress tank with closed copper coil. All of these give good results where the jacket or coil is properly constructed, the steam trap is of the right type and takes care of all of the condensation without allowing it to back up into the coil, and the kettle has a good head of steam so that a vigorous boil can be maintained throughout the cooking.

Steam Pressure

If the steam pressure at the boiler is kept above 75 lbs., and too much is not lost by radiation from uncovered pipes, and by leaks at poorly packed flanges, etc., there should be no difficulty in maintaining a vigorous boil. The evaporation should be so rapid that the vaporizing steam will burn the hand, even if placed over the kettle for a second. If you can hold your hand over a kettle of boiling pulp, even for a few seconds, you can be sure that you are not getting a proper boil. A pressure of 100 lbs. is, of course, to be preferred to 75, as it will effect a quicker condensation, however there is not a large percentage of boilers in tomato pulp plants that are permitted to carry as much as 100 lbs.

The kettles should be close to the boiler room, and the steam pipes feeding them should be as straight and short as possible, and covered with magnesia pipe covering to prevent excessive loss of heat by radiation. It is not an uncommon sight in canning plants to see the main pipe from the boiler to the cooking kettles pass through an areaway between two buildings, and have no protective covering whatever. Such sights, however, are becoming more infrequent, as packers are plugging up many of the leaks through which dollars have escaped every day in years gone by. The condensation from the steam traps can, of course, be used right over again in the boilers.

Copper-Jacketed Kettles

Copper-jacketed kettles used for condensing tomato products range all the way from 50 gallons capacity to 500 gallons, the larger size making a batch of finished pulp of about 250 gallons as a rule. A larger batch than this can be cooked in a 500–gallon kettle, but it is not advisable to keep pumping fresh tomato juice into the kettle too long, as it gives too long a cook to the first that goes in. Forty-five minutes should be the absolute limit for a batch of pulp, no matter what kind of a kettle it is cooked in, and it is much better to confine the cooking time to 30 minutes or less. The shorter the cook, the better the color and flavor of the finished product, other things being equal.

Tinning Kettles

Copper kettles are frequently lined with block tin to prevent the acid of the tomato from dissolving some of the copper. The desirability of this is argued both from a standpoint of health and flavor, as dissolved copper, even in small quantity, has a very bitter taste. It should be remembered, however, that the acid of the tomato, which is generally thought to be citric acid, is a weak organic acid, and the amount of copper dissolved in a batch cooked not over an hour is exceedingly small; certainly so small as to have no ill effect upon health. As to the question of flavor, it would indeed take a very delicate palate to detect among a half dozen samples which ones were cooked in an unlined copper kettle, and which in a kettle lined with block tin or silver. The latter is said to be used by some packers.

It is a good idea, however, to play safe, and line all kettles with block tin, as we know that there is a small amount of copper taken up in solution in the pulp. This is more important in the case of catsup and chili sauce than where the kettles are used for pulp alone, as vinegar and salt act on the copper much more severely than tomato acid does. As to the thickness of the block tin lining, an inspection of the kettles used by various packers shows this to run all the way from a good half-inch thick to a coating so thin that in one season’s use it is almost all scraped off by friction in cleaning the kettle. The kettles should be plated heavy enough to last several seasons without re-tinning, however a coating a half-inch thick is unnecessary and wasteful of steam. The same remarks apply to the tinning of copper coils.

Advantages of Various Types of Kettles

Although copper-jacketed kettles have the advantage of being very easily cleaned, and also the advantage of wasting very little of the product when the finished batch is being discharged, the large tanks of either cypress or glass-lined steel are coming into use more and more because of their greater capacity. It is true that they are very slightly more wasteful than the jacketed kettles, but this really amounts to very little if the tanks are built with a concave bottom. They take up no more room than the jacketed kettles, and will hold a much larger volume, as they can be built so much higher. If one were to buy a series of copper-jacketed kettles to cook batches as large as are commonly cooked in tanks equipped with copper coils, the expense would be very heavy, there would be much exposure to metal, and the results obtained would be no better, or possibly not as good. In the tank equipped with a coil, batches of 300 or 400 gallons are often cooked, and the juice can generally be condensed to a specific gravity of 1.035 in 25 to 30 minutes.

Glass-Lined Tank

During the last few years quite a few packers, when adding to their cooking capacity, have put in glass-lined steel tanks. The glass-lined tank is equipped with coil and steam trap in the same manner as the cypress tank, and it has certain advantages which make it very nice to work with, even though the first cost is considerably more than that of a cypress tank of equal capacity. The only objection I have heard to the glass-lined tank is that it radiates more heat than a wooden tank, and on very hot days, unless it is insulated, makes the cook room more uncomfortable than the same capacity in cypress tanks would. However, when the tank is covered with cork insulation, or asbestos, or even wood staves, it radiates no more heat than a cypress tank.

The glass-lined tank is perfectly sanitary, and is very easily cleaned. It is really the most sanitary thing we have to cook in. The surface is smooth and entirely free from any irregularities such as there are bound to be between the staves of the cypress tank. It is always ready for use, and does not have to be swelled and then scrubbed for a half day after standing idle for a while before it is fit to use again. There are no places for molds to creep in and multiply. Furthermore, being of metal and all in one piece, a battery of glass-lined tanks will not shake like cypress tanks will when you are running heavy and have several tanks going full blast at the same time. This may seem rather unimportant, but it is quite a relief to the cook and his helpers, as they can go about their work without having their nerves rattled. Just how long a glass-lined tank will last under average conditions in a pulp or catsup plant is not known, as they have not been in use a great many years for this purpose; however, one would guess that they would be serviceable almost indefinitely.

Cypress Tank

Cypress tanks should be constructed of 2–inch material and made with a sloping or concave bottom, preferably the latter. They will not impart any foreign taste to the product, as is sometimes thought, even after becoming charred by long usage, and if kept clean they will remain sweet as long as they are kept in continuous use. A musty taste is sometimes imparted to pulp or catsup cooked in a cypress tank if it has been standing idle for a long time and is not thoroughly cleaned and boiled out with soda before it is used again. Cypress tanks have the advantage of being cheap, and also of having large cooking capacity.

Cleaning Kettles

Cooking tanks and kettles should be cleaned thoroughly after every batch. If the steam trap is working properly the burning on the coils and sides of the kettle will be so slight that almost all of it can be washed off with the hose if the water pressure is strong and the hose is bushed down to one-eighth inch. The best things to use to take off the material which burns on hard and black is a pot chain for coils, and for the jacketed kettles a wire brush or very stiff fiber brush does very well. If any of the baked on pulp is not removed before the next batch is cooked it will interfere with the cooking by lengthening the time required to finish the batch, and by causing the coils to burn still harder next time. The cook should be instructed to get down in the tanks frequently, and feel underneath his coils to see that they are properly cleaned. The manager should also make it a point to do this several times a day. His quality will depend in no small degree on the way his coils are cleaned.

Coil Leaks

Leaks in coils should be attended to immediately, as they cut down the available steam pressure, and soon become so large that it becomes impossible to cook satisfactorily. An ordinary soldering job will only hold them for a day or two, and it is necessary to take out the coil and braze it if the leak is to be permanently mended.

Starting the Cooking

We will say that we are now pumping over the cycloned or crushed tomatoes into the cooking kettle. Some packers pour a cupful of cottonseed oil in the kettle to assist in breaking the boil, others rub the sides of the kettle with fat, such as a piece of cocoa butter, while others use no oil or fat at all, but take care to feed the kettle slowly and carefully, and cut the foam with a sharp spray of water from the hose to assist in breaking the boil. The oil or fat does seem to help some, but it is not necessary if the kettle is fed carefully. As soon as the coil or jacket is covered the steam can be turned on full; however, the exhaust should be opened immediately, and not closed until all the condensation which has collected in the coil or jacket runs out and the steam comes through perfectly dry. The condensation of the pulp should then be conducted as rapidly as possible, pumping over more of the tomato juice as the kettle is able to take care of it, and boiling continuously. The eye soon learns to judge the approach of the finishing point, and then the exact finishing point must be determined. There are many ways of doing this, and a number of ways have been recommended. No method can succeed which is not simple and quick, and which offers scarcely any chance for error when used by a cook, whom, it must be remembered, is a man of very ordinary intelligence.

Methods of Gauging Finishing Point

The simplest method is gauging the finishing point by the eye, but this method is also the least accurate in the hands of the average cook. Cooks who have had years of experience with tomato pulp sometimes get to be very expert in gauging the finishing point by the eye, and can determine it with surprising accuracy. Such a cook is the exception, however, and most packers have to use some sort of a mechanical method by which at least fair accuracy can be counted on. These methods consist of: first, condensing the pulp to a certain mark on the kettle, a definite volume of juice having been taken to start with; second, cooking a certain length of time; third, determining the specific gravity of the hot pulp by weighing a definite quantity on a small balance; fourth, estimating the gravity by the use of a hydrometer.

Cooking to a Gauge on Kettle

With the first method the amount of tomato juice pumped into the kettle, or the number of bushels of tomatoes from which this juice was derived, must be measured. This is a nuisance, and is not necessary with any of the other methods except the second. Furthermore, even though every batch of pulp cooked during the season be made from a measured quantity of tomatoes or tomato juice, and cooked to the same point on the measuring stick, the pulp will not all be of the same specific gravity, because tomatoes are very watery at some seasons of the year and very firm and solid at other times. The watery tomatoes will make a thin pulp, and the firm tomatoes will make a heavier pulp.

Cooking a Definite Length of Time

Cooking for a certain length of time is not dependable because the steam pressure is not always the same, the coils do not always condense the pulp with the same efficiency, and the character of the tomatoes varies during the season. With this method it is also necessary to start with a definite quantity of tomato stock for each batch.

Determining Specific Gravity by Weight

The third method—that of determining the specific gravity by weight—is used as commonly as any of the others. The specific gravity of pulp merely means the comparison between the weight of a definite volume of the pulp and the weight of the same volume of water at the same temperature. If pulp has a specific gravity of 1.035, that means that a gallon of it is 1.035 times as heavy as a gallon of water.

The determination, as carried out in the cook room, is made with a small trip balance, a set of weights, and a copper flask which is tin lined. The weight of the empty flask is taken. Then the weight of the flask filled to the top with boiling water is taken. The difference between these two weights is the weight of water at the boiling point which the flask contains. When the boiling pulp approaches the finishing point, the flask is filled to the top with the boiling pulp. This should be done rapidly, as the pulp cools quickly, and as it cools, decreases in volume. The weight of the flask filled with pulp at the boiling point is taken. This weight, minus the weight of the empty flask, equals the weight of pulp at the boiling point which the flask contains. You now have the weight of boiling water the flask contains, and the weight of boiling pulp the flask contains. Divide the former into the latter, and the result (the quotient) is the specific gravity. For example, if the water weighs 1,000 grams, and the pulp weighs 1,035 grams, the specific gravity is 1.035. If the specific gravity of cold pulp is taken, then cold water of the same temperature must be taken as the comparison. The weight of cold pulp must not be compared with the weight of hot water, and vice versa.

Objections to Weighing Method

One of the objections to the use of this method is that there is usually a certain amount of air bubbles and foam in the boiling pulp and this causes an error, as the air takes up volume but does not weigh anything. Another objection is that the determination is often not made rapidly enough, with the result that while the flask is being filled with boiling pulp, the pulp is cooling and correspondingly decreasing in volume, and by the time the flask is full, it contains more pulp than it should, that is, instead of containing 1,000 cubic centimeters of pulp at 210 degrees F., it will contain about 1,010 cubic centimeters of pulp at 200 degrees F., or possibly lower. One reason for this delay is that the foam caused by filling the flask with boiling pulp rises in the neck of the flask, and makes it hard to judge when the flask is exactly full. The main difficulty with the method, however, is that pulp cooks do not have scientific minds, they do not appreciate the importance of doing the determination in a strictly scientific way, and the results they get are not very accurate. I have frequently checked up on pulp cooks using this method, and sometimes they were very decidedly off.

Testing With Hydrometer

The estimation of the gravity of the boiling pulp by the use of a hydrometer is not in very general use, and it has been stated by some scientific men that a hydrometer is no good for tomato pulp or catsup except where the sample on which the test is made is previously filtered so as to get a clear liquid. A test which involves filtering, is, in my opinion, entirely unsuited for everyday use on the cooking platform.

I have used the hydrometer for testing pulp and catsup direct from the kettle for seven years, and have had more success with this method than with any other.

The hydrometer was never intended to be used with semi-solid substances such as tomato pulp, but only with liquids such as brine, sugar syrup, etc., in which there is no solid matter in suspension. With liquids, the number of degrees registered on the hydrometer when it is immersed in the liquid is equal to a definite specific gravity. This is not true with semi-solids such as tomato pulp, as each packer must work out the relation between the degrees of the hydrometer and the specific gravity on pulp under the conditions which obtain in his plant. This is a very simple thing to do, and once the packer has established this relation, it will hold good as long as he is in the pulp packing business. The reason why this relation is not the same for all packers is because tomato juice is not screened to the same degrees of fineness in all plants, and because all hydrometers having the same scale will not work the same on pulp. This is because they have different shapes. The shapes may only vary slightly, which will not interfere with their accuracy on clear liquids, but it will make a difference when the hydrometer is used in tomato pulp. Furthermore, some of the hydrometers will probably have too much variation in their diameter at different points, which is a disadvantage when they are used in tomato pulp. I have therefore always had the hydrometers which I have used for this test made to order and to conform to certain specifications which I laid down.

In Fig. 3 is illustrated a hydrometer which is manufactured by the C. J. Tagliabue Mfg. Co. of Brooklyn, and which is made to conform to these specifications, which are: first, perfect balance; second, a minimum amount of variation in the diameter of the various parts of the spindle with the slope very gradual; third, a Beaume scale reading from 0 to 50 degrees; fourth, that it can be obtained in exact duplicate in any quantity.

If the diameter at various points in the spindle is slight, with the slope very gradual, it seems to be an advantage. It is, of course, necessary that exact duplicates can be obtained to use when the first one, on which your calculations are based, is broken.

In order to avoid disappointments which would be very apt to result from the use of a hydrometer which was not particularly adapted to this test, and which would very likely be difficult of exact duplication, the type illustrated above should be adhered to, and it will be found to give good results when used as directed in this chapter.

Two pulps of the same specific gravity, and of practically the same degree of fineness, if tested hot, will register the same on the same hydrometer, or on two hydrometers which are exactly alike in every respect. (The hydrometer does not work well on cold pulp unless the pulp is thin.)

Two pulps of the same specific gravity, showing a very marked difference in their degree of fineness, will not register the same on the same hydrometer, because, even though a definite volume of each will weigh the same, the two pulps are of different thicknesses, which will have an effect on the degree to which the hydrometer will sink when placed in the pulp. However, if a packer cyclones his tomatoes before condensing them, and uses the same mesh of wire screen in his cyclone all the time, his pulp will all be of the same degree of fineness, and this point is eliminated. Every pulp packer who cyclones his tomatoes, and who uses the same mesh of screen in his cyclone throughout the season, can use the hydrometer for testing his pulp and can obtain uniformity without the use of any complex apparatus.

The relation between the hydrometer reading and the desired specific gravity is arrived at as follows:

When the boiling pulp approaches the finishing point, pour a sample into a tall gallon measure and take the hydrometer reading immediately. Save this sample, put it through the finishing machine along with several additional gallons dipped from the kettle so as to get a good sized sample through the finisher, taking care that the brushes are dry so as not to dilute the sample, and have the specific gravity determined on this finished sample when it gets cold. Take other samples from the kettle at five-minute intervals, and save them for the same purpose, after getting the hydrometer reading. We will say that one of these samples, when tested for specific gravity, ran 1.035. The packer looks up the hydrometer reading he got on this sample, when taken hot from the kettle, and finds the reading was 18 degrees. He then knows that for pulp of the degree of fineness he gets from his cyclone, 18 degrees on his hydrometer equals specific gravity 1.035 after finishing. He may also find that for the sample that was taken from the kettle five minutes later, specific gravity 1.04 is equivalent to 24 degrees under the same conditions. He now has established a relation between the degrees on his hydrometer and the actual specific gravity. (The reason for putting the pulp through a finisher before determining the specific gravity is that he wants to make this test under the same conditions that the buyer would make it.)

Now, if the packer decides that he wants to condense his season’s run of pulp to 1.035, he simply cooks it all to 18 degrees on his hydrometer, providing this is the comparison he got. Under his conditions he may find that 16 or 20 degrees equals specific gravity 1.035. As stated before, each packer must determine this for himself.

Method of Using Hydrometer

The cook should fill a tall gallon measure with the boiling pulp and allow the spindle to sink into it slowly. Do not drop it into the pulp so that it will fall suddenly, as the weight of the mercury or shot in the bottom will carry it farther than it should go. It will be noticed that the spindle will sink rapidly for a few seconds and then almost come to a standstill. At this point—when a standstill is almost reached—the reading should be taken. It requires quite a little time to reach an absolute standstill, and this is not necessary, as it is easy, with a little practice, to catch the other point and take the reading. After the reading is taken, lift out the spindle, stir the pulp with it, and allow it to sink again as a check determination, merely for the satisfaction of being doubly sure. You will find that you get the same reading unless you wait so long before making the check determination that the sample has had a chance to cool considerably. As the test only takes ten seconds, the two tests can be made in a half minute at the most, which gives the pulp no chance to cool.

The hydrometer method is not absolutely fool proof, but it is as near fool proof as anything I know of. Neither is it the acme of perfection in a pulp testing method, but it is, in my opinion, far better than anything that has been suggested to date. It is simple, and accurate enough for all practical purposes, and any ordinary laborer can be shown in a few minutes how to make the test, and the chances of error are very small indeed.

This method will not work where crushed tomatoes are being condensed. It is necessary that the tomato juice be previously cycloned. The pulp must be homogeneous and not lumpy and full of skins to be capable of being tested by the direct hydrometer method. When determining the finishing point on crushed tomatoes it is best to use either the eye or the specific gravity test by weighing.

Finishing the Cooking

The steam should be kept on the kettle continuously until the batch is done. While testing is being done it is not necessary to shut off the steam. If salt is used it should be scattered over the batch slowly a few minutes before it is done. Salt increases the specific gravity, and also the hydrometer reading. The relation between the hydrometer reading and the specific gravity can be worked out just as well where salt is used as when it is not used.

The addition of salt does add to the flavor, and some buyers prefer it, while others do not. I have seen buyers pick out a poor quality pulp with salt in it in preference to a much better quality with no salt.

As soon as the steam valve is closed the exhaust should be opened to discharge the steam from the coil or jacket and allow it to cool as quickly as possible.

It is often necessary to hold batches in the cooking kettles for some time after the cooking is finished. This darkens the pulp some, both because of contact with the air, while hot, and from long contact with the sides of the kettle or coil, which remain hot. Cooked pulp should therefore be discharged from the kettle just as soon as possible. If held over 30 minutes in the kettle it should be given a momentary boil before letting it down. Be careful to avoid contamination in the kettle after the steam is shut off, such as cold dirty water dripping in from rafters overhead, and leaks from pipes over the kettles through which cold tomato juice is flowing. Such material will not become sterilized merely by contact with the hot pulp, and may cause swells in the canned product if there is very much of it.